The present invention relates to a lock system. More particularly this invention concerns such a system wherein a plurality of locks which can be operated by respective keys that cannot operate the other locks can all be also operated by a single master key.
Lock systems are known and in common use which employ a plurality of similarly constructed locks which each have a respective key for operating the respective lock and none of the other locks. In addition such a system includes a master key that can operate all of the locks. Such an arrangement is particularly advantageous in an apartment building so that each tenant can be provided with his or her own key that opens only his or her own apartment. The custodial staff nonetheless can be provided with a single master key that serves to open any of the apartment doors, thereby eliminating the necessity of carrying a great many different keys.
Typically such a system simply uses split pin tumblers in the locks so that each lock can be operated by two differently bitted keys. Such a system can be produced at relatively low cost, but has the concomitant disadvantage that a person having a subordinate key, that is a key other than the master key, can relatively easily ascertain just what the bitting is for the master key and appriately file down his or her subordinate key to produce such a master key.
It has also been suggested to profile the master and subordinate keys differently. In all such arrangements the master key has a cross-sectional area which is smaller than that of any of the subordinate keys, so that this master key can fit into the slot of a subordinate key, but the subordinate key cannot fit into the slot of a master lock designed to open only for the master key. Typically, this is accomplished by forming one or more ridges along the sides of the blade of the key. Such a ridge is normally spaced from the guide edge of the key, that is, the edge opposite the bitted edge of the blade thereof. Most generally the blade of the master key except for the region immediately adjacent its guide edge is simply flat, so that a would-be burglar or the like need merely file his or her subordinate key flat in order for it to fit into the master-only key slot.
Another disadvantage of such systems is that they adapt themselves relatively poorly to systems wherein it is desired to submaster some of the locks, that is, provide a subgroup of locks which can all be opened with a single submaster key that can nonetheless not open any of the other locks of this system. Of course, in such a submastered system there is still one overall master key which can open any lock of the system, and there is normally at least one lock which can be opened only by the master key.